In conventional electric vehicles such as an electric vehicle or hybrid vehicle capable of traveling by means of its own electric motor, a large-capacity storage battery (drive battery) for the vehicle is provided which can store a large amount of high-voltage electric power for driving the electric motor and which is charged by electric power supplied from an external charging apparatus located outside of the vehicle. The drive battery is provided with contactors for on/off of supplying electric power from the external charging apparatus.
Also, in this type of electric vehicle, when the vehicle is put into operation, an SOC (State of charge), which indicates the remaining capacity of the drive battery, is detected from the open circuit voltage of the drive battery, and in addition, failure diagnosis is performed by opening and closing the contactors provided in the drive battery, to detect adhesion of the contactors and electric leak in the drive battery.
A power supply system using an electric vehicle has been developed in which, in order to secure operability of an externally connected device such as electrical equipment at home or a household electrical appliance in cases where the supply of electric power from an electric power provider is unavailable at the time of disaster, for example, or where the vehicle is at a place away from home and there is no power supply available, the externally connected device is connected to the vehicle being parked, and the high-voltage electric power stored in the drive battery of the vehicle is supplied to the externally connected device (Patent Document 1).